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| Do you model pole-mounted XFMR differently? https://brainfiller.com/arcflashforum/viewtopic.php?f=23&t=6074 |
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| Author: | BarkFlash [ Mon May 12, 2025 12:21 pm ] |
| Post subject: | Do you model pole-mounted XFMR differently? |
Say we have 3 single-phase pole mounted 75kVA transformers that together form a 3-phase Delta-Wye system. Would you model those separately? If you model it as one single transformer, what kVA do you use? We have a disagreement in the office about what the equivalent KVA should be for 3-75kVA transformers connected to form a distribution system. Should the equivalent be: a) 75 b) SQRT(3)*75, or c) 3*75 If you model those 3XFMR's separately in SKM, do you get the same result as your answer above? |
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| Author: | JBD [ Mon May 12, 2025 12:29 pm ] |
| Post subject: | Re: Do you model pole-mounted XFMR differently? |
A bank of single transformers is consider as a single three phase transformer, if they are all the same size and impedance. (3) 75kVA units equals (1) 225kVA unit. |
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| Author: | bbaumer [ Mon May 12, 2025 3:31 pm ] |
| Post subject: | Re: Do you model pole-mounted XFMR differently? |
JBD wrote: A bank of single transformers is consider as a single three phase transformer, if they are all the same size and impedance. (3) 75kVA units equals (1) 225kVA unit. ^^^^ This ^^^^ Also note that the %Z does NOT triple and will likely be much lower than a typical 3 phase transformer. Those single phase cans are more like 1.2%, not 4 or 5% or so. This means your secondary available fault current will be higher than it is with a typical 3 phase unit. |
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